Electrochemical and quantum chemical studies of cetylpyridinium bromide modified carbon electrode interface for sensor applications
Introduction
Neurotransmitters are referred to as chemical messengers capable of neurotransmission. More than 40 neurotransmitters exist in the human nervous system. Among these, dopamine (DA) is one of the most important chemicals that play a significant role in human brain performing specific functions such as movement, memory, emotional control, sleep and attention. In recent years, extensive research has focused on DA detection. It is found that the abnormal level of DA can cause severe neurological diseases, for example of Azheimer's and Parkinson's [[1], [2], [3], [4], [5]]. In particular, due to its portable advantage, the electrochemical analytical technique stands out as a powerful method for detecting the level of DA. However, in the human body uric acid (UA) and DA co-exist, and their values of voltammetric oxidation are close to each other. Therefore, there is an increasing demand for methodological development towards simultaneous detection of DA and UA.
In voltammetric measurements, carbon paste electrodes (CPEs) are the most frequently used materials for the electrochemical working electrode. The advantages of CPEs include wide electrochemical window, low background current, and easy to miniaturize [6,7]. In particular, the performance efficiency of bare CPE (BCPE) strongly depends on its surface structure [8,9]. As such, the main disadvantages for such electrodes are weak mechanical stability and low sensitivity while operating in analytical processes [8,10]. To overcome these limitations, surface modification of BCPE has been developed and among these being adopted approaches, surfactant immobilization represents an economical means [8].
In general, surfactants are amphiphilic compounds with hydrophilic and hydrophobic parts [11]. Based on the characteristic, the ability of the electrode surface to adsorb analytes can be enhanced, leading to voltammmetric signals increased [[12], [13], [14]]. Surfactants are also able to adsorb onto the electrode surface in the monolayer fashion [15,16]. Depending on the intrinsic ionic strength of the surfactants, the polarity of these layers can largely affect charge transfer rates and the redox potential in electrochemical measurements, giving rise to positive effect in sensing [17]. Surfactants commonly used to modify electrodes include Triton-X-100 [18], cetyltrimethylammonium bromide [19], sodium dodecyl sulfate (SDS) [20] and Cetyl pyridinium bromide (CPB). The latter is a water-soluble cationic surfactant with pyridinium cation (hydrophobic) as a head with a hydrocarbon chain (hydrophobic) as a tail. To date, very few studies have been done about CPB modified CPE (CPBMCPE) compared to other cationic surfactants modified electrodes [21,22].
Presumably, surfactant at the CPE interface can provide additional active sites for electron transfer (ET) reactions [8,23]. Higher numbers of analytes on a surfactant-modified CPE surface has been expected to undergo electron transfer reactions and thus lead to the increase in voltammetric signals. Hence, such electrodes in principle can be considered as better electrochemical sensors compared to bare CPE. To comprehend this electrochemical phenomenon, a more in-depth understanding merits special attention. An approach to this end is the analysis from the perspective of the Conceptual Density Functional Theory (Conceptual DFT [24]) based on Quantum chemical calculations [8,9,23,24]. Modeling of CPBMCPE interface is meaningful because it can reveal the CPB arrangement and, unveil the location of energy levels and the electron transfer sites. To our knowledge, there is no literature related this topic. In this contribution, we model CPB on bare CPE surface and locate electron transfer sites by the conceptual DFT based on the frontier molecular orbital approximation (FMO) for obtaining Fukui functions. To quantify global reactivity, hardness, softness, electron-donating and electron-accepting powers were computed by means of the Auxiliary Density Perturbation Theory (ADPT) [25].
Section snippets
Reagents and chemicals
Cetylpyridinium bromide (CPB), benzethonium chloride (BzTC), cetyltrimethyl ammonium bromide (CTAB) were purchased from Sigma Aldrich (TM), graphite powder, DA, UA, potassium chloride, and perchloric acid were obtained from Himedia (TM), sodium dihydrogen phosphate and disodium hydrogen phosphate was used for the preparation of 0.1 M phosphate buffer solution (PBS). All chemicals and reagents were used as they received and prepared with distilled water.
Instrumentation
Cyclic voltammetric experiments were
Quantum chemical modeling and fabrication of CPBMCPE
Theoretical modeling of surfactants is useful in Electrochemistry [9,43,44]. The shapes of the surfactants are dependent on the solvent media, temperature, critical micellar concentrations, etc. We are modeling surfactants in a vacuum, and there will not be any significant dipole-dipole interaction. Therefore there will be fewer possibilities for the rotation of surfactants aliphatic tail. Previously, several theoretical studies obtained the energy minima of surfactants with the extended
Conclusion
In conclusion, CPBMCPEs have been fabricated by CPB immobilizations on the bare CPE surface. Such electrodes are found promising for the simultaneous detection of DA and UA and present excellent CV responses with decreased oxidation overpotential and enhanced peak currents for DA and UA. The electrodes were further applied to the determination of UA in urine samples and satisfactory results obtained. Through this work, we have understood the underlying molecular phenomenon, namely how CPB can
CRediT authorship contribution statement
Gururaj Kudur Jayaprakash: Conceptualization, Investigation, Formal analysis, Writing - original draft, Writing - review & editing. B.E. Kumara Swamy: Conceptualization, Supervision, Writing - review & editing. Juan Pablo Mojica Sánchez: Formal analysis, Writing - review & editing. Xiuting Li: Writing - review & editing. S.C. Sharma: Writing - review & editing. Shern-Long Lee: Supervision, Writing - review & editing.
Acknowledgment
G.K.J thankful to Dr. Jayaram Kowshik Bettadapura, Post-Doctoral Researcher, Yau Mathamatical Sciences Centre, Tsinghua University, Beijing, P.R. China, and Scientific Writing Cell of Shoolini University for useful discussion. Authors G.K.J. and J.P.M.S. are very thankful to Professor Roberto Flores-Moreno, Department of Chemistry, University of Guadalajara for the useful discussion on the theoretical studies of the work. All authors are thankful to the reviewers for new and useful comments.
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